As a biomagnetism measuring system of medical equipment, for example, a magnetoencephalography system has been known. The magnetoencephalography system measures a weak magnetic field generated by brain neurons from the outside, and inspects an active portion in a brain and a degree of the activation thereof with high accuracy.
This type of biomagnetism measuring system includes a high-sensitivity magnetism measuring device. As the high-sensitivity magnetism measuring device capable of detecting a weak biovector magnetic field such as brain magnetism, a superconducting quantum interference device (SQUID) has been used, but a cryogenic environment is necessary for its operation.
On the other hand, as a high-sensitivity magnetic field measuring device which can operate in the atmospheric air at a normal temperature, a diamond crystal which includes nitrogen-vacancy pairs has been proposed (for example, see S. Steinert, F. Dolde, P. Neumann, A. Aird, B. Naydenov, G. Balasubramanian, F. Jelezko, and J. Wrachtrup; “High sensitivity magnetic imaging using an array of spins in diamond”, Review of Scientific Instrument 81, 043705-1˜5, (2010) (Non-Patent Document 1)).
In the Non-Patent Document 1, the following contents are disclosed. A green laser beam is used as a viridian light source which irradiates the diamond crystal serving as a sensor to measure the magnetic field with an excitation light, and a charge coupled device (CCD) image sensor is used to detect a red fluorescent output from the diamond crystal. The magnetic field is measured from a position of the microwave frequency at a minimum fluorescence intensity in a microwave frequency dependency of a red fluorescence intensity acquired by sweeping the frequency of the microwave emitted to the diamond crystal.